1. Field of the Invention
This invention relates to containers, and, in particular, to multi-layer sheet materials for sealing containers.
2. Discussion of the Prior Art
Sheets of multi-layered materials have been used to prepare innerseals to seal the openings of containers from air and contaminants. A simple innerseal consists of a sheet of metal foil bearing a layer of heat sealable material for bonding the foil to the lip of a container, for example, a bottle. Innerseals are typically die-cut from sheets of a multi-layered material and sealed by means of heat to the lip of the container.
Innerseals can be constructed to have a tab that extends outwardly from the periphery of the innerseal so that a user can grasp the tab to aid in removing the innerseal from the container.
An innerseal having a tab is typically employed with a container having a threaded neck, which container employs a threaded cap. The innerseal is die-cut from the aforementioned multi-layered sheet of metal foil bearing a layer of heat sealable material. The tab is folded 180.degree. so that it can fit within the cap but still be in such a position that it can later be used to peel the sealed innerseal off the lip of the container. The innerseal is then inserted into the cap, and the cap is twisted onto the neck of the container. The capped container is then heated by means of induction to heat the aluminum foil and thereby melt the layer of heat sealable material so that the innerseal will be bonded to the container. Innerseals having tabs can also be used with containers that employ snap-on caps.
U.S. Pat. Nos. 4,047,473 and 4,155,439 describe a method and apparatus for applying sealing membranes having a folded pull tab to containers. The patents describe the apparatus for die-cutting the sealing membranes from a sheet, folding the tab, and inserting the sealing membranes into an overcap. The overcap assembly is then placed on the container, tightened, and the sealing membrane is sealed to the container.
U.S. Pat. No. 4,754,890 describes a tamper evident safety seal having a tab that consists of a sheet material that is folded in a Z or S configuration to form a double folded tab. The safety seal can also include a scrim to provide additional strength.
U.S. Pat. No. 4,625,875 describes a tamper evident safety seal that includes a cap and a sealing disc having a tab.
Although sealing membranes, safety seals, sealing discs, and innerseals having tabs for easy removal are known in the art, the tab may have certain deficiencies that prevent innerseals having tabs from receiving widespread acceptance in the marketplace. When the innerseal is die-cut, the edge of the innerseal adjacent to the tab can become nicked, so that when the user pulls on the tab, only a portion of the innerseal may be removed. If the innerseal has poor internal strength, when the tab is pulled, only a narrow strip of innerseal material, having a width substantially the same as the width of the tab, is removed. In some cases, the tab can be pulled off without removing any part of the innerseal.
Another problem encountered with innerseals currently used in the marketplace is referred to herein as springback. In most conventional innerseals, after the tab is folded to allow insertion of the innerseal in the cap, the tab springs back about 90.degree. so that rather than laying flat against the portion of the innerseal covering the mouth of the container, it extends roughly perpendicular to the plane of the innerseal. After the innerseal is inserted into the cap, springback of the tab can push the innerseal out of the cap and cause it to be misaligned during sealing so that an inadequate seal is formed. Springback of the tab can also cause the innerseal to fall out of the cap, resulting in an unsealed container.
It would be desirable to provide an innerseal having high internal strength and further having a tab that exhibits springback of less than about 45.degree. from the plane of the innerseal once the tab is folded against the portion of the innerseal covering the mouth of the container. As stated previously, conventional innerseals typically spring back about 90.degree. from the plane of the innerseal.